The vulnerable UPnP stack is used in many routers based on Broadcom chipsets, DefenseCode researchers say.

Security researchers from Croatia-based security firm DefenseCode claim to have found a critical remote code execution vulnerability in the UPnP (Universal Plug and Play) implementation developed by Broadcom and used by many routers with Broadcom chipsets.

The UPnP standard defines a set of networking protocols that allow devices to discover each other and automatically establish working configurations to enable data sharing, media streaming, media playback control and more. The UPnP service is intended to be used on local networks, but Rapid7 found that there are over 80 million devices on the Internet that respond to UPnP discovery requests, making them vulnerable to remote attacks.

The Broadcom UPnP implementation contains a format string vulnerability that can be exploited by sending a specifically crafted SOAP (Simple Object Access Protocol) request to it, the DefenseCode researchers said in an advisory published Wednesday.

The vulnerability can be exploited to read the memory of a device that uses the vulnerable Broadcom UPnP stack or to write arbitrary values at arbitrary addresses in its memory. If exploited correctly, the vulnerability allows an unauthenticated attacker to execute arbitrary code with root (administrator) privileges on the device, they said.

DefenseCode's researchers originally discovered this vulnerability in the Cisco Linksys WRT54GL router model and reported it to Cisco earlier this month. However, they later realized that the vulnerability is actually located in the Broadcom UPnP stack and most likely affects other Cisco routers, as well as routers from other manufacturers.

Broadcom, Asus, TP-Link, Netgear and D-Link did not immediately respond to a request for comment.

Cisco already developed a fix for the vulnerability reported in the WRT54GL model and is working with DefenseCode to validate it, a Cisco representative said Friday via email. "The fix will be released for customers as soon as possible, but in the meantime those using the WRT54GL can stay safe by ensuring their wireless network is securely configured, and the only people using an Ethernet cable for connecting to the router are friends," according to the Cisco official.

The Cisco Product Security Incident Response Team (PSIRT) is investigating DefenseCode's claim that additional Cisco products, including WRT54G3G and WRT310N, might be vulnerable, but nothing can be confirmed at this time, the Cisco representative said.